Plants respond to pathogen attack by mounting a complex defense response that is mediated by different signaling events, among which is the generation of reactive oxygen species (ROS). The current model is that ROS, namely superoxide and its dismutation product, hydrogen peroxide, together with nitric oxide interact in a concentration-dependent manner to initiate downstream defense pathways. The long term objective of this proposed research is to dissect the ROS-dependent pathways responsible for initiating programmed cell death, inhibition of pathogen colonization, systemic acquired resistance, and basal defense responses in all plants using Arabidopsis thaliana Col-0 and Pseudomonas syringae pv. tomato DC3000 as a model system. Knowledge of these ROS-mediated pathways in plants can be applied to animal systems to bridge the gap between animal and plant immunological responses. Furthermore, increased knowledge of plant disease resistance directly benefits agricultural practices, which can significantly benefit human health through enhanced food production.